1. Field of the Invention
This invention relates to a light weight shaped opaque aluminum borate product. More particularly, this invention relates to a high strength, light weight, shaped opaque aluminum borate product formed by reacting an aluminum oxide and a boron oxide and a method of making the aluminum borate material using an improved sintering aid.
2. Description of the Related Art
Lightweight ceramic materials formed from aluminum oxide mixed with phases of other metal oxides are desirable from the standpoint of weight as well as chemical inertness. In Ray U.S. patent application Ser. No. 604,913, there is described and claimed a ceramic which comprises an interwoven mixture of TiB.sub.2 and Al.sub.2 O.sub.3 formed by reacting together a mixture of TiO.sub.2, B.sub.2 O.sub.3 and aluminum metal. This ceramic material has been found to possess excellent electrical conductivity and chemical inertness properties even at elevated temperatures, making it an excellent material for use as an electrode in an electrolytic reduction cell at elevated temperatures.
However, such ceramic materials or cermets are not necessarily characterized by light weight nor do they always possess high strength qualities, particularly if they have been blended to optimize other properties such as chemical inertness and electrical conductivity.
The formulation of ceramic materials from oxides of aluminum and boron would be expected to be somewhat lighter than aluminum oxide, depending upon the amount of boron oxide used, since the density of aluminum oxide is about 3.9 and the density of boron oxide is about 2.46. Ceramics made from such oxides are known.
Sowman U.S. Pat. No. 3,795,524 describes the formation of transparent extrusions such as fibers of aluminum borate and aluminum borosilicate materials from an aqueous solution or dispersion, e.g., an aqueous solution of a boric acid-stabilized aluminum acetate, which is concentrated into extrudable gels, subsequently dried, and then fired at temperatures up to 1000.degree. C. to form fibers of transparent aluminum borate or aluminum borosilicate. The patentee states that low density aluminum borate fibers may be formed in this manner having an Al.sub.2 O.sub.3 :B.sub.2 O.sub.3 mole ratio of from 9:2 to 3:1.5. Sowman, however, cautions against firing at temperatures as high as 1200.degree. C., stating that fibers fired at this temperature are weak and fragile.
DeAngelis U.S. Pat. No. 4,540,475 discloses the formation of a multiple phase body containing phases of TiB.sub.2, Al.sub.2 O.sub.3 and 9Al.sub.2 O.sub.3 2B.sub.2 O.sub.3 which was formed from a dry mixture of AlB.sub.2, TiO.sub.2 and Al.sub.2 O.sub.3 which was pressed at 1500 psi and then fired at 1500.degree. C.
Baumann and Moore in an article entitled "Electric Furnace Boroaluminate" in The Journal of the American Ceramic Society, Oct. 1, 1942, Vol. 25, No. 14, disclose that boroaluminate has been produced as a crystalline material by electric furnace fusion. The crystal form is orthorhombic, and it appears to melt incongruently and is analogous in several ways to mullite.